1. Field of the Invention
The present invention relates to an accessory device such as a video light and a microphone, and more particularly to an accessory device equipped with a connection mechanism which is connected to and fixed on an image pickup apparatus such as a video camera.
2. Description of the Related Art
Conventionally, various types of connection mechanisms which are configured to connect an external accessory device to an accessory shoe of a camera main body (hereinafter referred to as an “accessory shoe”) to be fixed have been proposed.
The connection mechanism connected to and fixed on the accessory shoe has a function as a communication means for communicating various kinds of signals with the camera main body, in addition to a mechanical function which fixes the accessory device itself on the camera main body. Therefore, in order to ensure a reliable communication path, with regard to the connection mechanism of the accessory device, the connection position relation with the accessory shoe with high accuracy needs to be maintained.
In order to prevent the connection state between the connection mechanism of the accessory device and the accessory shoe from easily being released, for example, the following configuration is adopted as a connection mechanism.
First, in order to perform a positioning of the accessory device, a locking pin which can be removably inserted into a joint hole formed on the accessory shoe is provided. Second, a shoe locknut which sets a firm fixing state is provided by the screw connection with respect to a shoe base provided on the lower part of the accessory device which constitutes the connection mechanism and by moving in an upward and downward direction by rotation to fasten the accessory shoe.
FIG. 17 shows a main cross-sectional view of a connection mechanism in a conventional accessory device.
In FIG. 17, shoe locknut 3 is connected by a screw with respect to a shoe base 2 fixed on a lower part of a main body 1 of an accessory device. The shoe locknut 3 itself moves in an upward and downward direction by rotation of the shoe locknut 3.
A locking pin 4 inserted into a joint hole formed on an accessory shoe (not shown) is provided movably in an upward and downward direction in a through hole which is configured to pass through the shoe base 2 in an upward and downward direction. One end part 4a is connected to one end part 5a of a spring 5 in the main body 1.
A base part 5b of the spring 5 is fixed on the main body 1 and always biases the locking pin 4 in a direction where the other end part 4b protrudes outside the shoe base 2, i.e. in a direction where the other end part 4b protrudes outside the shoe base 2 and is inserted into an engagement hole formed on the accessory shoe.
A protrusion 6 passes through a lower part of the main body 1 and is positioned between the shoe locknut 3 and the spring 5. One end part 6a of the protrusion 6 protrudes outside the main body 1 in accordance with the relation of the position where it is in contact with an upper end surface of the shoe locknut 3. The other end part 6b of the protrusion 6 is provided so as to be in contact with the spring 5. When the shoe locknut 3 is rotated so as to move in an upward direction for releasing the connection, the upper end surface is in contact with the one end part 6a of the protrusion 6.
When the shoe locknut 3 is further rotated so as to move in the upward direction in this contact state, the protrusion 6 presses the spring 5 against its biasing force via the other end part 6b in the upward direction. The locking pin 4 connected to the one end part 5a of the spring 5 moves in the upward direction by the spring 5 pressed in the upward direction. As a result, the joint with the joint hole which is formed on the accessory shoe is released.
On the other hand, when the shoe locknut 3 is rotated in a direction opposite to the case described above, the shoe locknut 3 moves in a downward direction.
The spring 5 moves the protrusion 6 and the locking pin 4 in the downward direction by its elastic force. Therefore, the one end part 4b of the locking pin 4 is protruded outside the shoe base 2 and is inserted into the joint hole formed on the accessory shoe (not shown). Thus, the position relationship between the accessory device and the camera main body is set in a specific state.
In this case, in accordance with the movement of the above shoe locknut 3 in the downward direction, a part of the accessory shoe (not shown) is clipped by the shoe base 2 to be fastened. Therefore, the shoe base 2 is fixed on the accessory shoe and the accessory device is firmly fixed on the camera main body.
In other words, the locking pin 4 moves in the upward and downward direction via the elastic force of the spring 5 in conjunction with the movement of the shoe locknut 3 in the upward and downward direction. Therefore, the accessory device is positioned with respect to the camera main body by the locking pin 4 and the joint hole formed on the accessory shoe.
Reference numeral 7 denotes a plurality of signal pins which are electrically connected to each kind of signal terminals formed on the accessory shoe (not shown).
On the other hand, since the shoe locknut 3 rotates to move in the upward direction and an end surface of the shoe locknut 3 is in contact with an end surface of the main body 1, further rotation of the shoe locknut 3 is limited.
When a rotational force which moves the shoe locknut 3 in the upward direction is further added to the shoe locknut 3, a bite unnecessary for the screw connection between the shoe locknut 3 and the shoe base 2 may occurs. If the bite unnecessary for the screw connection occurs, the shoe locknut 3 can not rotate there and it may take a long time for the release of the rotation disable state in the next movement in the downward direction.
In order to avoid such an inconvenience, for example, the configuration of a stopper mechanism as disclosed in Japanese Examined Utility Model Application Publication No. 57-29045 has been proposed. This stopper mechanism (not shown) has the following configuration. In other words, it includes a C-shaped groove formed on either one of an end surface of the facing shoe locknut and an end surface of the main body 1 (a groove that is planarly formed in a C-shape where a circumferentially-formed groove is partially blocked) and a protrusion provided on the end surface of the other one. Here, when the end surface of the shoe locknut gets close to the end surface of the main body 1, the rotation of the shoe locknut stops by contact of the protrusion on an end wall part in the C-shaped groove.
By the way, according to the connection mechanism in the conventional accessory device shown in FIG. 17, the accessory device and the camera main body can maintain the relationship of the connection position with high accuracy and can be firmly connected to each other.
However, since each of the locking pin 4, the spring 5, and the protrusion 6 is an independent part, a plane area to some extent is necessary for the arrangement of the parts and the miniaturization of the connection mechanism is limited.
Since the locking pin 4 and the like are independent parts, the influence of the variation in size of each of the parts is large. For example, it is difficult to maintain the operating position of the shoe locknut 3 that is an operating member and the moving state of the locking pin 4 to be in a desired relation with high accuracy.
Furthermore, if the configuration for avoiding the bite as disclosed in Japanese Examined Utility Model Application Publication No. 57-29045 attempts to be provided as it is, it is necessary to ensure an arrangement space for the protrusion 6 or a protrusion which is in contact with an end surface of a C-shaped groove between an end surface of the shoe locknut 3 and an end surface of the main body 1.
Accordingly, as described above, in conjunction with the need of the plane area to some extent, the shape of the connection mechanism may grow in size. Therefore, it was a large problem in view of the miniaturization of devices.
On the other hand, Japanese Patent Laid-Open No. discloses that the operation of moving up and down of the locking pin is performed using a cam. However, in this configuration, a cam member other than the shoe locknut needs to be prepared. Therefore, the number of the parts can not be drastically reduced.